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Measurement of the production cross section for a W boson in association with a charm quark in proton-proton collisions at = 13 TeV
No full textInternational audienceThe strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis uses a data sample corresponding to a total integrated luminosity of 138 fb collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged using the presence of a muon or a secondary vertex inside the jet. The W+c production cross section and the cross section ratio = (W+)/(W+) are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay. The precision of the measurements is improved with respect to previous studies, reaching 1% in . The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics
A second-order model of small-strain incompatible elasticity
No full textInternational audienceThis work deals with the modeling of solid continua undergoing incompatible deformations due to the presence of microscopic defects like dislocations. Our approach relies on a geometrical description of the medium by the strain tensor and the representation of internal efforts using zero-th and second-order strain gradients in an infinitesimal framework. At the same time, energetic arguments allow to monitor the corresponding moduli. We provide mathematical and numerical results to support these ideas in the framework of isotropic constitutive laws
States, symmetries and correlators of and symmetric orbifolds
No full textInternational audienceWe derive various properties of symmetric product orbifolds of and - deformed CFTs from a field-theoretical perspective. First, we generalise the known formula for the torus partition function of a symmetric orbifold theory in terms of the one of the seed to non-conformal two-dimensional QFTs; specialising this to seed and - deformed CFTs reproduces previous results in the literature. Second, we show that the single-trace and deformations preserve the Virasoro and Kac-Moody symmetries of the undeformed symmetric product orbifold CFT, including their fractional counterparts, as well as the KdV charges. Finally, we discuss correlation functions in these theories. By extending a previously-proposed basis of operators for - deformed CFTs to the single-trace case, we explicitly compute the correlation functions of both untwisted and twisted-sector operators and compare them to an appropriate set of holographic correlators. Our derivations are based mainly on Hilbert space techniques and completely avoid the use of conformal invariance, which is not present in these models
Multispecies cross-diffusions: from a nonlocal mean-field to a porous medium system without self-diffusion
No full textInternational audienceSystems describing the long-range interaction between individuals have attracted a lot of attention in the last years, in particular in relation with living systems. These systems are quadratic, written under the form of transport equations with a nonlocal self-generated drift. We establish the localisation limit, that is the convergence of nonlocal to local systems, when the range of interaction tends to 0. These theoretical results are sustained by numerical simulations. The major new feature in our analysis is that we do not need diffusion to gain compactness, at odd with the existing literature. The central compactness result is provided by a full rank assumption on the interaction kernels. In turn, we prove existence of weak solutions for the resulting system, a cross-diffusion system of quadratic type
Persistent components in Canny's Generalized Characteristic Polynomial
No full textInternational audienceWhen using resultants for elimination, one standard issue is that the resultant vanishes if the variety contains components of dimension larger than the expected dimension. J. Canny proposed an elegant construction, generalized characteristic polynomial, to address this issue by symbolically perturbing the system before the resultant computation. Such perturbed resultant would typically involve artefact components only loosely related to the geometry of the variety of interest. For removing these components, J.M. Rojas proposed to take the greatest common divisor of the results of two different perturbations. In this paper, we investigate this construction, and show that the extra components persistent under taking different perturbations must come either from singularities or from positive-dimensional fibers
A Novel Integer Linear Programming Approach for Global L0 Minimization
No full textInternational audienceGiven a vector y ∈ R n and a matrix H ∈ R n×m , the sparse approximation problem P 0/p asks for a point x such that ∥y-Hx∥ p ≤ α, for a given scalar α, minimizing the size of the support ∥x∥ 0 := #{j | x j ̸ = 0}. Existing convex mixed-integer programming formulations for P 0/p are of a kind referred to as "big-M ", meaning that they involve the use of a bound M on the values of x. When a proper value for M is not known beforehand, these formulations are not exact, in the sense that they may fail to recover the wanted global minimizer. In this work, we study the polytopes arising from these formulations and derive valid inequalities for them. We first use these inequalities to design a branch-and-cut algorithm for these models. Additionally, we prove that these inequalities are sufficient to describe the set of feasible supports for P 0/p. Based on this result, we introduce a new (and the first to our knowledge) M-independent integer linear programming formulation for P 0/p , which guarantees the recovery of the global minimizer. We propose a practical approach to tackle this formulation, which has exponentially many constraints. The proposed methods are then compared in computational experimentation to test their potential practical contribution
Criticality safety of fuel assemblies with missing fuel rods
No full textInternational audienceThe present work is concerned with the problem of determining the reactivity of an assembly from which an unknown number of fuel pins are removed at random locations. Because it is usually designed to be under-moderated, the reactivity of an incomplete assembly will pass by an optimum when the number and position of the missing rods vary. Estimating this maximal reactivity is paramount for criticality safety but is difficult to achieve in practice, because of a prohibitive combinatorial factor, that forbids any direct approach of the problem. It is shown that the maximum reactivity of an isolated PWR assembly with missing fuel rods can be estimated with very few calls on time expensive computer simulations. Drawing a parallel with the field of neutron transport in random geometries, it is indeed shown that the problem can be reduced to an optimum search in an appropriate bounded, bi-dimensional space
Search for the lepton flavor violating 3 decay in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for the lepton flavor violating 3 decay is performed using proton-proton collision events at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2017-2018, corresponding to an integrated luminosity of 97.7 fb. Tau leptons produced in both heavy-flavor hadron and W boson decays are exploited in the analysis. No evidence for the decay is observed. The results of this search are combined with an earlier null result based on data collected in 2016 to obtain a total integrated luminosity of 131 fb. The observed (expected) upper limits on the branching fraction ( 3) at confidence levels of 90 and 95% are 2.910 (2.410) and 3.610 (3.010), respectively
Momentum scale calibration of the LHCb spectrometer
No full textInternational audienceFor accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of collected during 2016 in running. The procedure uses large samples of and decays and leads to a relative accuracy of on the momentum scale
The Extraordinary March 2022 East Antarctica "Heat" Wave. Part II: Impacts on the Antarctic Ice Sheet
No full textInternational audienceBetween March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) which caused these record-shattering temperature anomalies. Here in Part II, we continue our large, collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt which was recorded along coastal areas, but this was outweighed by widespread, high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Finally, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea-ice extent